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For many car owners, an oil dipstick is just a tool to check the lubricant level in the engine. However, this seemingly simple engine component can provide valuable information about its condition, especially in the case of older vehicles.

To identify these potential problems, you can perform an oil check while the engine is running. In addition, similar information can be obtained by unscrewing the oil filler cap on the cylinder head cover while the engine is running. The engine is running and the driver pulls the oil dipstick out of its socket. In a properly functioning engine, the driver should be able to do this with some slight resistance, which is caused by the crankcase ventilation system creating a slight vacuum inside the engine crankcase and under the cylinder head cover.

This vacuum ensures that gases leaving the combustion chambers do not accumulate inside the engine, but are directed into the intake manifold. From there they flow back into the cylinders and eventually exit through the exhaust pipe. A special valve, primarily a membrane, is responsible for creating this suction, which regulates the level of vacuum in the crankcase.

Over time, this diaphragm can fail and the valve can become stuck open. This leads to uncontrolled suction of oil from the engine into the combustion chambers. If the oil dipstick is difficult to pull out while the engine is running, as if someone is holding it by the other end, that’s usually good news too. This resistance often indicates that the engine’s internals are fine and the problem is most likely with the crankcase ventilation valve. If the dipstick literally almost flies out on its own, then it’s time to contact a service center and be prepared for serious repairs.

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